The general aim of this research proposal is to develop an effective treatment intervention for individuals who meet criteria for both drug use disorders and for borderline personality disorder (BPD). Specific aims are to pilot test and modify as needed an existing cognitive behavioral treatment (Dialectical Behavior Therapy; DBT) which has been shown to be effective for severely dysfunctional, chronically suicidal women who meet criteria for BPD. We will also develop and pilot an assessment battery for evaluating treatment with this population. To accomplish these objectives, we plan to conduct a one year pilot treatment outcome study with approximately 20 subjects meeting criteria for both drug use disorder and for BPD. Subjects will be randomly assigned to a DBT pilot treatment condition (n=10) or to a community treatment-as-usual (TAU) condition (n=10). Outcomes targeted and measured will include reductions in frequency and severity of substance abuse, suicidal behaviors, therapy-interfering behaviors, dysfunctional behaviors (other than substance abuse and suicidal behaviors) that severely limit the quality of life and negative affect and enhancement of general functioning and interpersonal skills. DBT therapists will be the PI as well as experienced psychotherapists and drug abuse counselors trained in DBT by the PI. The major outcome assessment battery will be administered at pre-, 4-month, 8-month, and 12-month points (immediately following the end of treatment) treatment points. Additional daily patient ratings, weekly client and therapist ratings by DBT subjects and random drug testing for all subjects will be conducted. Observation of treatment sessions (through one-way mirrors and by video), weekly case consultation meetings, and ongoing assessments will be used to monitor and document treatment delivery and make necessary changes to the treatment and assessment protocols.